(1) Field of the Invention
The present invention relates to an on-demand system, such as a VOD (Video On-Demand) system, by which information and services can be utilized immediately after requesting the information and/or services.
(2) Description of the Related Art
A VOD system which is a type of on-demand system is formed as shown in FIG. 1. As shown in FIG. 1, an ATM-SW unit (ATM switching unit) is connected with a video server and a plurality of video STB terminals. The video server stores video information items of various video programs. In response to a selecting request of a video program from a subscriber, the video server supplies a video information item corresponding to the requested video program to the subscriber. The video information items are generally compressed, for example, in accordance with a specification of the MPEG-2. Each of the STB (Set Top Box) terminals is a transmitter-receiver terminal unit which is mounted on a television unit of a subscriber. Each of the STB terminals transmits control signals, such as a signal for requesting to televise a video program, to the video server and decodes the video information received from the video server. The ATM-SW unit has a SVC (Switched Virtual Connection) function as a dynamic routing so that a path can be set between a calling terminal and a called terminal in accordance with a dialing operation of a subscriber. The service of the dynamic switching function has to be usually supplied by a switching unit having a grade not less than a grade of the ATM edge switching unit.
In the VOD system, in response to a selecting request of a video program from a subscriber (a STB terminal), the ATM-SW unit has to connect the video server and the STB terminal. In this case, a subscriber dials the video server in which a program favorite with the subscriber is stored so that the STB terminal of the subscriber carries out a calling process. The ATM-SW unit sets a path between the STB terminal of the subscriber and the called video server so as to connect them to each other. If the video server accepts the selecting request of the video program, the video server transmits the video information corresponding to the video program. As has been described above, in the conventional VOD system, it is necessary to provide the ATM-SW unit having a dial-up-signaling function (the SVC function).
The ATM-SW unit is expensive, so that the production cost of the on-demand system using the ATM-SW unit as has been described above is high. Thus, it is preferable that the STB terminals and the video server are connected using a connection unit which is cheaper than the ATM-SW unit so that the on-demand system can be constructed at a lower cost.
An ATM-HUB unit is known as the connection unit for the ATM. As shown in FIG. 2, the ATM-HUB unit is often used in a star connection formation as the backbone of the communication between LANs via LAN units. In many cases, the ATM-HUB unit has only a PVC (Permanent Virtual Connection) function based on input commands, but does not have the SVC function as the dynamic routing. Thus, in general, the ATM-HUB unit can not be applied to services, such as a VOD service and a video telephone service, which needs the dynamic routing function of a switching unit. There is a type of ATM-HUB unit which partially has the switching function. However, the switching function is not sufficient to supply the on-demand service.